Partial defloeeulation of mutual floes of allophane and halloysite by xanthan and chitosan and relevance to particle arrangement in the floes

Abstract

Deffocculation of mutually flocculated allophane and halloysite at pH 5 in the presence of gum xanthan (GX) and chit os an (CS) was investigated using an optical method. Montmorillonite was used as a reference clay. In agreement with previous findings, anionic GX-polymer flocculated the positively charged allophane. On the other hand, dispersion of allophane and flocculation of halloysite and montmorillonite in the presence of CS in dilute acetic acid solution at pH 5 indicated that CS behaved as a cationic polymer. Positively charged allophane and negatively charged halloysite (and also montmorillonite) formed complete mutual flocs at pH 5 at certain mass ratios. When the average diameter of the montmorillonite and halloysite particles was smaller than that of the allophane particles in suspension, the mutual flocs deflocculated slightly by the addition of CS at an extremely low concentration (ca. 10-4 g L-1), but did not deflocculate in the presence of GX. On the other hand, in the case of the larger particles of halloysite, the mutual flocs deflocculated moderately by the addition of GX, but did not deflocculate in the presence of CS. It was concluded that the partial deflocculation of the mutual flocs with GX and CS at an extremely low concentration was due to polymer adsorption onto the outer surface of the flocs, caused a decay (separation) of the mutual flocs. For the particle arrangement associated with partial deflocculation of the mutual flocs, two models were suggested: (1) smaller halloysite (and also montmorillonite) particles should be located around the flocculated allophane, and (2) larger halloysite particles should be located in the center of the mutual flocs.